Light extinction measurements have been used since the late 1800's to quantify aerosol characteristics such as visual range, number concentration and mass concentration These measurement techniques, first developed by Tyndall and Lord Rayleigh, have improved to the point where light extinction is routinely used to determine compliance with the Environmental Protection Agency Clean Air Act requirements.
Light extinction is given by the basic form of the Lambert-Beer law EQU I/I.sub.O =exp (-.sigma.L) (1)
where
I=Transmitted light intensity measured through the aerosol PA1 I.sub.O =Transmitted light intensity measured without the aerosol PA1 .sigma.=extinction coefficient of the aerosol (cm.sup.-1) PA1 L=path length of the light beam through aerosol (cm). PA1 D=geometric particle diameter (cm) PA1 Q=extinction coefficient of the particle PA1 N=particle number concentration (cm.sup.-3)
For a monodisperse aerosol containing N particles per cubic centimeter EQU .sigma.=(N.pi.QD.sup.2)/4 (2)
where
Aerosol characteristics, i.e. visual range, number or mass concentration, cannot be explicitly calculated from extinction data because usually two or more of the parameters in equation (2) are unknown. Therefore, assumptions, estimations, and correlations must be employed to infer aerosol characteristics from light extinction measurements. As described in "On the Generality of Correlation of Atmospheric Aerosol Mass Concentration and Light Scatter" by R. J. Charlson, N. C. Alquist, and H. Horvath, Atmospheric Environment, 2:455-464 (1968), these approximations work reasonably well for a well characterized, stable system such as ambient atmospheric aerosol. The approximations are not valid for a less stable system such as stack emissions, due to instabilities with respect to size distribution and aerosol composition. For these types of systems, light extinction measurements can only be valid on a case by case basis after the specific aerosol has been characterized, as noted by M. J. Pilat and D. S. Ensor in "Plume Opacity and Particulate Mass Concentration" Atmospheric Environment, 4:162-173 (1970).
For aerosols such as those released by severe fuel damage to nuclear reactor fuel, the aerosol composition is not well known, much less well characterized, and the aerosol release is necessarily transient. In such a case, conventional light extinction measurements cannot be used to determine number concentration or mass concentration without assuming values for the particle size and extinction coefficients.
Accordingly, it is an object of the present invention to provide a light extinction apparatus and method to determine the number concentration of an aerosol without assuming values for the particle size and extinction coefficient.
It is a further object of this invention to determine number concentration of an aerosol in an cost effective accurate manner.
It is a still further object of this invention to determine estimates for particle size, aerosol mass concentration, and aerosol mass flow rate in a light extinction apparatus.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.